Selection Guidelines - Convert DC Wall Wart to AC Wall Wart

V

Vons Garage

New Member
It seems I have no shortage of DC power adaptors - at all! Occasionally I need an AC version; for example, clocks requiring 60Hz for time base.

Given a needed AC voltage, which DC power adaptor voltage rating would you experts select to break open, pull out all the DC conversion components, retain just the transformer, and then glue the whole thing back together again?

Should you try to match the desired final AC voltage exactly? Or select one that has a higher or lower voltage than the target?

And finally, your opinions: what do you think these things should be officially called: external power supplies, power adapters, AC adapters, or power bricks? Has anyone come up with a more elegant name than “wall wart” that clearly identifies these type that actually have the guts at the point-of-connection to the mains?
 
Sort by date Sort by votes
To calculate the AC voltage for a wall wart, measure the DC voltage with no load and divide by 1.414. That will give the no load AC voltage. Under the rated load (same load as DC rating) the AC voltage may drop a bit, but not as much as it does at DC mode.
Find a power device that gives the required AC voltage, plus or minus a volt or so. Most devices requiring AC rectify it to DC internally anyway, except devices that need 60Hz for things like motors.
 
Upvote 0 Downvote
You need to know what the requirements of the clock you're trying to feed are - although I've never seen (or heard of) a wall wart AC powered clock?.

Bear in mind as well, most wall warts are switch mode, you would need to find one that uses a conventional mains transformer, and quite probably one that's unregulated as well (most regulated ones are switch-mode).
 
Upvote 0 Downvote
Sagor1: Noted, printed out, and added to my piles and piles of DC supplies for future reference. Cool.

Mr. Goodwin: per manual: Power consumption: About 5.7 watts, (0.6 amps @ 9.5 volts AC)
Try this link: https://transistorclock.com/
This cool kit, made by KABtronics, is no longer available. What a build it was back when I got it!
Someone has cloned it's design. Check eBay for Mega Transistor Clock.
And I will bear in mind about the different varieties of supplies. Probably by hefting them!
 
Upvote 0 Downvote
A switch mode supply won't work for this. There is no line frequency transformer.

You need an old-school linear supply. These will be heavy for their size, and roughly "regular" cube shaped – roughly equal size in all 3 dimensions, not thin and flat.
 
Upvote 0 Downvote
I would suspect any DC wall wart that gives 12.5 to 14.5VDC with no load will do. Getting 0.6A will require a heavier transformer unit, always verify the current capacity.
The picture you show, shows a bridge rectifier (4 diodes) in the lower left corner, so most of the clock would run off about +12V. The AC voltage is just to get the 60Hz for the clock sync. There don't seem to be any voltage regulators or IC chips, just transistors, so it just runs off the approx. +12VDC
 
Upvote 0 Downvote
For The Popcorn said:
A switch mode supply won't work for this. There is no line frequency transformer.

You need an old-school linear supply. These will be heavy for their size,
Click to expand...
This is the main thing to look for, the weight. Linear power supplies that use line-frequency transformers are heavy. They are also increasingly rare.
 
Upvote 0 Downvote
Thanks all for the additional information. I understand I am looking for these power adaptors that are old school transformer equipped. Can anyone think of a foolproof way to identify these ole' rascals? A compass? A magnet?
 
Upvote 0 Downvote
They will tend to be ice-cube shaped, often with ventilation slots. The most common ones will be around 3" in the long direction

Low voltage output AC supplies are also available in this form.



 
Upvote 0 Downvote
Vons Garage said:
Thanks all for the additional information. I understand I am looking for these power adaptors that are old school transformer equipped. Can anyone think of a foolproof way to identify these ole' rascals? A compass? A magnet?
Click to expand...
In addition to the above, look at the input voltage, If it's a single voltage (like the one in post #13,) or a narrow range, ie. 110-120VAC then it's most likely to be what you want.

But if it's a wide range, ie. 90-250VAC, then it'll be a smps type.
 
Upvote 0 Downvote
You must log in or register to reply here.

Similar threads

increase in voltage on wall adapter
Replies
13
Views
3K
MrAl
M
C
Components for AC-DC rectifier
Replies
13
Views
3K
danadak
K
  • Solved
How to evaluate DC motor controller
Replies
6
Views
2K
koyote
K
  • Question Question
AC Blower Motor Speed Control
Replies
4
Views
590
ahsrabrifat
A
D
  • Question Question
Combine two AC-DC adaptors to increase the amps
Replies
7
Views
4K
DerZauss
D
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…